The configuration of human teeth requires that the ideal bristle contour for toothbrushes for brushing the buccal or outside surfaces of teeth be concave and that the ideal bristle contour for brushing the lingual or inside surfaces of teeth be convex. Most brushes have a single piece head which is of comparable thickness to the handle and which is relatively rigid and of a fixed curvature or configuration.
A further drawback of conventional brushes is that pressing the brush sufficiently hard against the teeth to get good cleaning risks damaging or discomforting the softer, adjacent gums. To a certain extent this can be solved by modifying the configuration of the brush, or by varying bristle hardness or length, though again, a single configuration cannot be optimum for all circumstances.
Some brushes may, however, incorporate a means for allowing the head to flex relative to the handle, as described for example in EP-A-371,293. Even so, such brushes have limited effectiveness. Other brushes are known which are adjustable into several different but fixed configurations. Adjustable toothbrushes are often difficult to manipulate and may be unreliable.
U.S. Pat. No. 4,712,267 discloses a convertible toothbrush comprising an S-shaped elongated handle of shape-retaining material having curved end regions of opposite curvature, a flexible brush block containing bristles, and a means for mounting the flexible brush block on the handle for longitudinal movement along the length of the handle. The curved portions of the handle bend the flexible block and bristles into a concave or convex configuration which corresponds to the curved configuration of the handle.
EP-A-454,625 describes an adjustable curvature toothbrush whose head is in the form of a loop. A cam or slide mechanism changes the curvature of the head between concave and convex configurations. In an alternative embodiment, the head is an integral part of the handle which is in the form of a compressible closed loop, the bristle surface being in a concave configuration when the handle is in its uncompressed state, becoming convex when the handle is compressed.
The brushes of the two aforementioned documents require the user to set the brush head to one configuration or another. The brush head remains in that configuration until reset. U.S. Pat. No. 2,445,657 on the other hand describes a toothbrush with a single material resilient head, e.g. of vulcanised rubber, jointed to a handle. The head is continuously flexible and its curvature can be adjusted by pressing against the teeth, gums or cheek. It is more difficult however, with such a brush head, to manufacture the brush to the required flexibility and the softer head material required presents additional problems of affixing the bristles, relative to conventional brush head materials.
WO 92/17093 discloses a toothbrush having a handle and at one end thereof a bristle-bearing head, wherein the head is in the form of two or more segments flexibly and resiliently linked to each other and/or to the handle, one or more of the segments being bristle bearing. In one embodiment this is achieved by the use of transverse, and optionally longitudinal, grooves on the opposite face of the head to the bristles. The grooves can be wholly or partially filled with an elastomer. In another embodiment the handle extends into a frame into whose interior the head is resiliently linked and voids between the head and the frame may be filled with an elastomer. In all embodiments the bristles are inserted into conventional brush head materials e.g. polyamides and polypropylenes.
While the above toothbrushes provide brush heads with some degree of flexibility, none of them is entirely satisfactory. In particular, they require undue manipulation or skill on behalf of the user, a more complex assembly process or fail to teach how to assure long-term durability of the brush head through repeated flexing.
Where it is desired to manufacture the brush head from the primarily conventional materials used to hold bristles then, preferably, points of weakness e.g. grooves must be built into the head to permit the desired head flexibility. Through many cycles of repeated flexing, the brush head material can be prone to failure, i.e. breaking at the thinned, grooved parts of the head. Alternatively, where the grooves are filled with elastomer to control flexibility or for hygiene reasons, the bond between the elastomer and the head material can be prone to failure.
It has now been found that the durability of the brush head can be improved by ensuring that the brush head has grooves on each faces of the head with elastomer contained in the grooves of at least one face, with the head flexibility being limited to a flex angle of less than about 40.degree..
The durability of the brush head can further be improved by providing that hinges of the head material, which connect the segments of the head are located between opposing faces of the brush head and at a distance of at least about 10% of the depth of the head from each of the faces.
It is accordingly an object of this invention to provide a brush head which can flex resiliently and which has good long-term durability.
It is a further object of this invention to provide a toothbrush comprising such a brush head.